1. Field of the Invention
The present invention relates to a method for separating immunoglobulin G subclasses. More particularly, it relates to a method for separating immunoglobulin G subclasses with high efficiency and precision.
2. Discussion of the Background
Immunoglobulin G (hereinafter referred to simply as IgG) has a structural unit comprising pairs of identical heavy chains (H-chains) and light chains (L-chains) linked by disulfide bonds (S--S bonds) as the basic structure in the same manner as other immunoglobulins. It is further classified into a plurality of subclasses based on the types of H-chains. For example, human IgG is classified into subclasses IgG 1, IgG 2, IgG 3 and IgG 4 having H-chains of different structures such as .gamma.-1, .gamma.-2, .gamma.-3 and .gamma.-4, respectively. Likewise, mouse IgG is classified into subclasses IgG 1, IgG 2a, IgG 2b and IgG 3. Such IgG subclasses have different physiological activities against complements or against phagocytes, but their properties such as the molecular weights and stereostructures are similar to one another. Therefore, as a method for separating such subclasses, it has been common to employ a separation method by affinity chromatography utilizing the differences in the affinity to protein A produced by Staphylococcus. The molecular weight of IgG is said to be about 150,000.
However, such a method of separating subclasses by affinity chromatography by means of protein A has problems such that it is necessary to change the pH of the fluent and the operation is therefore cumbersome and time-consuming, IgG 3 does not bind to protein A, and the separation of subclasses is inadequate.